Think of each element as a student who wants to finish a “class” of 8 friends (the octet rule).
Rule of thumb:
The number of electrons lost equals the group number.
Example: Na (group 1) → Na⁺ (\$+1\$); Mg (group 2) → Mg²⁺ (\$+2\$).
The number of electrons gained equals \$18 -\$ group number.
Example: Cl (group 17) → Cl⁻ (\$-1\$); O (group 16) → O²⁻ (\$-2\$).
⚛️ This simple rule helps predict the charge of most common ions you’ll see in chemistry.
Metals are like students who give away friends to reach a popular group of 8.
Nonmetals are like students who invite friends to fill their empty spots.
Na⁺ (\$+1\$), K⁺ (\$+1\$), Ca²⁺ (\$+2\$), Mg²⁺ (\$+2\$), Cl⁻ (\$-1\$), Br⁻ (\$-1\$), F⁻ (\$-1\$), O²⁻ (\$-2\$), S²⁻ (\$-2\$).
Group 1 → +1, Group 2 → +2, Group 3 → +3, …, Group 17 → –1, Group 18 → 0.
| Group | Typical Elements | Common Ion | Charge |
|---|---|---|---|
| 1 | Li, Na, K, Rb, Cs, Fr | M⁺ | \$+1\$ |
| 2 | Be, Mg, Ca, Sr, Ba, Ra | M²⁺ | \$+2\$ |
| 13 | B, Al, Ga, In, Tl | M³⁺ | \$+3\$ |
| 14 | C, Si, Ge, Sn, Pb | M⁴⁺ | \$+4\$ |
| 15 | N, P, As, Sb, Bi | M³⁻ | \$-3\$ |
| 16 | O, S, Se, Te, Po | M²⁻ | \$-2\$ |
| 17 | F, Cl, Br, I, At | M⁻ | \$-1\$ |
| 18 | He, Ne, Ar, Kr, Xe, Rn | Neutral | \$0\$ |
💡 Remember: The group number tells you how many “friends” (valence electrons) an element has.
Metals give away those friends → positive charge.
Nonmetals invite friends → negative charge.
Noble gases already have a full set → stay neutral.
Keep this rule in mind, and you’ll be able to predict ion charges in most reactions! 🚀